Mold material for casting metals



Patented Dec. 12, 1939 UNITED STATES cross REFERENCE PATENT OFFICE MOLDMATERIAL FOR CASTING METALS George 0. Clark, Beverly Hills, Calif.

No Drawing. Application August 5, 1938,

Serial No. 223,277

. Claims. (01. 22-18:) L

This invention relates to improvements in compositions for castingmetals and more particularly to the use of one form of mica as theprincipal component'part of molds in which metals are cast.

An important object of this invention is to pro-' vide a new compositionof matter for casting metal objects. The material is a form of micawhich is of a compressible yielding character and which when used asmolding material forms a porous non-fracturing body with smooth slightlyyielding faces against which the metal lies. The new composition ofmatter employed for casting metals is expanded mica or mica which has sotreated that the individual particles have lost their natural flakycondition and instead have a soft yielding granular character verysimilar to that of sawdust. Suitable binder material is provided forcohering the particles of expanded mica together and when a mold of thischaracter is dried as by a baking process it forms a sumciently strongmold capable of several hundred casting operations before becoming unfitfor use.

Heretofore, several attempts have beenmade to use mica in its naturalflaky state for lining or facing molds, for core material, or forforming a small component part of a mold mixture for casting metals. Noattempts however were made to use expanded mica, the particular form ofmica described herein, as either a minor or principal component part ofa mold mixture. Ex-

panded mica has distinctly diiferent characteristics from that ofnatural mica, characteristics which I have found lend themselvesespecially desirable for casting metals. A mold formed of thisparticular type of mica is suiiiciently flrm and indestructible so thatmany uniform .metal castings can be made from the same mold before themold becomes unflt for use. It provides, however, slightly yielding 'orelastic faces against which the molten metal lies which follow theexpansion and contraction of the metal as it hardens. Properties of thischaracter are not found when mica is used in molds in its natural state,

' whether in sheet, flaked or pulverized condition. The importantingredient of my invention, ex-- panded mica or vermiculite as it isknown in the trade, is formed by heat treating natural flaked mica sothat the stiff flaked state of the mica is destroyed and in its place asoft yielding granular form of mica is provided. One mode ofmanufacturing expanded mica is to convey relatively small sheets of micaof approximately one-halfto one inch square size through a furnace inwhich gas flames play on the mica sheets. In

this treatment the individual sheets or flakes of mica arepufled up orexploded into small curled granular particles of varying sizes similarin appearance and feel to that of sawdust. when compressed as betweenthe flngers, particles of expanded mica yield to the pressure andflatten out to a comparatively smooth surface conforming to the contourof the fingers between which they are pressed. This soft yieldingcharacteristic is present on the faces of molds of expanded mica yet thefaces are sumciently flrm so that when properly bonded by a suitablebinder and dried they will stand up for many casting operations. Moldsof this character are especially desirable for manufacturers who makemany castings of a given object and who do not desire to make a new moldfor each casting operation. I

Varioay be used to stick or hold fast the particles of expanded micawhile the mold takes an air set prior to baking and drying the same inan oven. Refractory binders such as silica clay, chrome clay, dextrin,and casein and those going imder the trade names of Eumnite apdHitempite uuu'nt 25 may be used. K preferred r' of a binder and expandedm is that in which the expanded mica forms approximately% to of themixture by volume.

In practice, it is desired to use expanded mica a of a substantiallyuniform size. Expanded mica between screenings of 30, and 60 mesh are tobe preferred but it is understood that the use of binder material aremixed thoroughly together before. use. The mixture is then compactlypressed around a pattern to form a mold cavity into which the moltenmetal will be poured. After the removal of the pattern the mixture 0holds its shape until it is heat treated and dried such as in a bakingoven. This removes the water content from the binder material used. Theresulting mold is' light, porous and yieldable but the particles ofexpanded mica are suflicientiy firmly coalesced together that they willnot chip or break down under the heat of the molten metal brought intocontact therewith. The face of the mold is not as soft andyieldable asthe 'face of wet sand molds which give at the lightest touch.Considerable finger pressure must be exerted to dent the surface of thepresent mold. 1

Prior to the pouring of the molten metal the 10 metal will lie closelyagainst the face of the mold thereby producing a coating thatcorresponds perfectly to -the contour of the pattern used in making themold.

The above described mold of expanded mica is 5 especially desirable forcasting lower melting point metals such as aluminum, bronze, copper, Dowmetal and others. It is understood, however, that the use of expandedmica in molds for casting higher meltingpoint metals is included 20within the purview of this invention. Many casting operations may beperformed by the same mold and up to several hundred uniform castingsfrom each mold may be expected without any cracking or fracturing of amold surface.

-as WhatIclaimis:

1. A mold to receive molten metal composed entirely of expanded micaparticles held together by a binder, and a facing for the mold cavitycomposed of expanded mica particles of finer size than that used in themold proper.

2. A mold to receive molten metal composed entirely of expanded micaparticles held together by a binder, and a facing for the mold cavitycomposed of a water mixture of finely ground graphite.

3. A mold to receive metal castings having a wall portion formed ofexpanded mica held together by a refractory binder and characterized asslightly yielding to pressure and sufliciently porous to permit escapetherethrough of gasses.

4. A mold to receive metal castings having a wall formed oLslightlyresilient expanded mica particles held together by a binder and porousto the escape of gas therethrough.

5. A mold to receive metal castings having a wall portion comprisingmica particles of soft yielding granular condition held together by abinder and being porous to the passage of gas therethrough, saidexpanded mica particles constituting 60% to 80% by volume of said wallstructure.

GEORGE C. CLARK.

